Computer room cooling system with bifurcated heated air return path

Abstract

A computer room cooling system having multiple branched heated air return paths for heated air generated by multiple rows of server racks 15C operating within a computer room 15 having a suspended ceiling plenum 16 and a heated air collection duct 14C, wherein a first heated air return path 61 routes heated air from a hot aisle duct 18 to the heated air collection duct 14C, and a second heated air return path 62 routes heated air from the hot aisle duct 18 to the high-volume suspended ceiling plenum 16 before the heated air is routed to the heated air collection duct 14C. A damper 20 with a mechanical thermostat 22 is used to control airflow between the hot aisle duct 18 and the high-volume suspended ceiling plenum 16.

Description

[Technical Field]

[0001] The present disclosure relates to a computer room cooling system, and more particularly to a computer room cooling system having a bifurcated heated air return path. [Background technology]

[0002] FIG. 1 is a block diagram illustrating a prior art heated air return path through a computer room 15. To aid in the description of items within the figure, FIG. 1 identifies several planar interfaces. The terms "plane" and "co-planar" used in this description are intended to describe a cross-sectional volume (either horizontal or vertical) within the computer room 15, rather than an ideal plane having no volume. A first horizontal plane 21 is coplanar with the upper surface of a false ceiling plenum (FCP) 16. A second horizontal plane 22-a is coplanar with the lower surface of the FCP of the false ceiling plenum 16, as well as with the cold aisle ceiling 15A1 of the cold aisle 15A and the hot aisle ceiling 15B1 of the hot aisle 15B. A third horizontal plane 23 is coplanar with the upper surface of a raised floor plenum 17. A fourth horizontal plane 24 is coplanar with the lower surface of the raised floor plenum 17. The first vertical plane 31 is flush with a first side of the hot aisle 15B. The second vertical plane 32 is flush with a second side of the hot aisle 15B. The third vertical plane 33 is flush with one side edge of the suspended ceiling plenum 16.

[0003] The computer room 15 in FIG. 1 includes a cold aisle 15A and a hot aisle 15B separated by a row of server racks 15C. The cold aisle 15A receives cooled air via a raised-floor plenum inlet 15D1-a and / or a fan wall inlet 15D1-b. The cooled air in the cold aisle 15A is drawn through the row of server racks 15C into the hot aisle 15B, where it is heated by the electronic equipment (e.g., servers and / or data storage devices) installed in the row of server racks 15C. The heated air is drawn from the hot aisle 15B through a hot aisle ceiling 15B1 (often constructed with perforated ceiling tiles in the prior art) into a suspended ceiling plenum 16 and returned to the air handling unit (AHU) 14C via a heated air collection duct (HACD) 14C and a heated air outlet (see 15D2 in FIG. 2). The heated air collection duct 14C is attached to a third vertical plane 33 on one side edge of the suspended ceiling plenum 16.

[0004] FIG. 2 is a block diagram illustrating a prior art dual-coil cooling system 10 for a computer room 15 using a free cooling tower 11 and a chiller 13. As in FIG. 1, the computer room 15 includes a cold aisle 15A and a hot aisle 15B separated by a row of server racks 15C. Cooled air from the air handling unit 14 is introduced into the cold aisle 15A via a cooled air inlet 15D1. The cooled air is drawn through the cold aisle 15A and heated by electronic equipment (e.g., servers and / or data storage devices) attached to the row of server racks 15C. The heated air is drawn back to the AHU 14 from the hot aisle 15B and cooled via a heated air outlet 15D2. The AHU 14 includes a free cooling coil 14A and a trim cooling coil 14B for cooling the heated air received from the hot aisle 15B. The free cooling coil 14A receives a first free refrigerant flow from the free cooling tower 11 to pre-cool the heated air. The trim cooling coil 14B receives a trim refrigerant flow from the evaporator passage 13B of the chiller 13 to further cool the heated air. The AHU includes a fan (not shown) for driving the heated and cooled air. The chiller 13 includes a condenser passage 13A that receives a second free refrigerant flow from the free cooling tower 11. The free cooling tower 11 receives ambient air 12 from the outside environment and cools the free refrigerant that is routed through (i) a first free refrigerant flow to the free cooling coil 14A of the AHU 14 and (ii) a second free refrigerant flow to the condenser passage 13A of the chiller 13.

[0005] The free cooling tower 11 derives its cooling benefits from the relatively low ambient air temperature of the external environment (compared to the heated air of the computer room 15) and the evaporation of water vapor within the free cooling tower 11. Therefore, the free cooling tower 11 is most efficient when interacting with the ambient air 12 of the external environment, which has both a relatively low temperature and low humidity (due to the greater evaporation of water vapor). The trim cooling coil 14B of the AHU 14 can be used to further cool the heated air of the computer room 15 located in a tropical or other high-humidity environment, but the chiller 13 requires significant power to function. Due to the high cooling costs of data centers located in tropical or other high-humidity environments, these companies must outsource their data computing to offshore data centers. Such offshoring can complicate the management of a business's data computing functions and complicate the business's procedures for complying with local data privacy regulations. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] US Patent Application Publication No. 2020 / 0396869 [Patent Document 2] U.S. Patent No. 7,716,939 [Patent Document 3] US Patent Application Publication No. 2019 / 0045669 Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, what is needed is a computer room cooling system that can maximize the efficiency of free cooling towers for computer rooms 15 operating in tropical or other high humidity environments.

[0008] Additionally, heat generation within the computer room 15 may fluctuate due to uneven computing needs during weekly or daily cycles, start-up of a new row of server racks 15C, maintenance schedules requiring server downtime, removal of old servers from the computer room 15, or revised business computing strategies. Therefore, what is needed is a computer room cooling system that can maintain high cooling efficiency despite daily, weekly, or monthly variations in heat load. [Means for solving the problem]

[0009] As described in the Detailed Description herein and illustrated in FIGS. 4A-6, the present invention employs a prior art damper 20. FIG. 3 is a block diagram illustrating a prior art damper 20 including a series of louvers 21 mechanically connected to a mechanical thermostat 22. The damper 20 is shown as viewed from a first side view 20-X along the length of the damper 20. The damper 20 is also shown as viewed from a second side view 20-Y along the width of the damper 20. Additionally, the damper 20 is shown in a top view 20-Z (mounted to the hot aisle ceiling 15B1 as described in the Detailed Description herein) as viewed from below. Note that, as described in the Detailed Description herein, the height of the damper 20 (e.g., as viewed from the first side view 20-X or the second side view 20-Y) can be mounted flush with one of the horizontal or vertical planes of the computer room 15 when installed in accordance with the present invention.

[0010] The damper 20 includes a series of louvers 21 configured to open and close when actuated by a mechanical connection to a mechanical thermostat 22. As the series of louvers 21 are twisted more open, the louver free area percentage of the damper 20 increases, reducing air resistance across the series of louvers 21 and thereby increasing the amount of variable airflow (e.g., cubic meters of air per minute) across the series of louvers 21 for a given pressure differential across the series of louvers 21. As the series of louvers 21 are twisted closed, the louver free area percentage of the damper 20 decreases, increasing air resistance across the series of louvers 21 and thereby decreasing the amount of variable airflow across the series of louvers 21 for a given pressure differential across the series of louvers 21.

[0011] After installation and during use, each mechanical thermostat 22 is exposed to adjacent heated air having an adjacent temperature. The mechanical thermostat 22 is attached to the side of the damper 20 exposed to the heated air (at an adjacent temperature) that is adjusted by opening and closing the series of louvers 21. The damper 20 can include multiple mechanical thermostats 22. The mechanical thermostats 22 do not need to be connected to a power source or networked as IoT devices. The mechanical thermostats 22 are configured to (1) increase the free louver area ratio of the series of louvers 21 mechanically connected to the mechanical thermostat 22 when the adjacent temperature of the mechanical thermostat 22 exceeds a preset threshold temperature of the mechanical thermostat 22, and (2) decrease the free louver area ratio of the series of louvers 21 mechanically connected to the mechanical thermostat 22 when the adjacent temperature of the mechanical thermostat 22 falls below the preset threshold temperature.

[0012] The set of dampers 20 can include preset thermostat settings including: (1) a preset threshold temperature, and (2) a minimum louver free area ratio for a preset minimum louver free area ratio for the set of louvers 21. The preset threshold temperature is the adjacent temperature at which the mechanical thermostat 22 twists the set of louvers 21 open, increasing the louver free area ratio and increasing the variable airflow across the damper 20. For example, if the preset threshold temperature is set to 40°C, the mechanical thermostat 22 will begin to further open the set of louvers 21 when the adjacent temperature of the mechanical thermostat 22 exceeds 40°C and will begin to further close the set of louvers 21 when the adjacent temperature of the mechanical thermostat 22 falls below 40°C. In this manner, each damper 20 can adjust the airflow across the damper 20 to maintain a general temperature range within the volume of air partially trapped by the damper 20 (assuming that higher airflow reduces the adjacent temperature of the air). Different sets of dampers 20 may have different preset thermostat settings (e.g., the preset thermostat settings may vary between sets of dampers 20, and not all sets of dampers 20 require the same preset thermostat settings).

[0013] The minimum louver free area ratio setting for a set of louvers 21 can act as a safety feature to avoid excessive heat buildup in the room and / or reduce the possibility of asphyxiation of working staff due to a lack of oxygen, carbon dioxide buildup, or other toxic gas buildup. For example, if damper 20 is preset with a minimum louver free area ratio of 10 percent, there will always be airflow across damper 20 (assuming there is a pressure differential across damper 20).

[0014] In its most general form, the present invention is a computer room cooling system having multiple branched heated air return paths for heated air generated by multiple rows of server racks operating in a computer room having a suspended ceiling plenum and a heated air collection duct. A first heated air return path delivers heated air from a hot aisle duct (HAD) to the heated air collection duct. A second heated air return path delivers heated air from the hot aisle duct to a high-volume suspended ceiling plenum before it is delivered to the heated air collection duct. A damper with a mechanical thermostat is used to control air flow between the hot aisle duct and the high-volume suspended ceiling plenum. The present invention can be used to maintain a minimum delta temperature between the heated air and a first free refrigerant flow received by an air handling unit from a free cooling tower operating in a high-humidity exterior environment.

[0015] A principal embodiment of the present invention is a computer room cooling system including a plurality of branched heated air return paths for heated air generated by a plurality of server rack rows operating in a computer room with a suspended ceiling plenum and a heated air collection duct, each branched heated air return path being associated with one server rack row in the computer room, one hot aisle located adjacent to the one server rack row, and one hot aisle duct located on the ceiling of the one hot aisle, and each branched heated air return path further including (i) a first heated air return path for heated air generated by the one server rack row, and (ii) a second heated air return path for heated air generated by the one server rack row. The first heated air return path proceeds as follows: (1) from the one row of server racks associated with the branched heated air return path, (2) into a hot aisle located adjacent to the one row of server racks, (3) through a plurality of first dampers attached to the ceiling of the one hot aisle, (4) into a hot aisle duct located above the ceiling of the one hot aisle, and (5) into the heated air collection duct. The second heated air return path proceeds as follows: (1) from the one row of server racks associated with the branched heated air return path, (2) into a hot aisle located adjacent to the one row of server racks, (3) through a plurality of first dampers mounted on the ceiling of the one hot aisle, (4) into a hot aisle duct located above the ceiling of the one hot aisle, (5) through a plurality of second dampers mounted on the side or top of the one hot aisle duct, (6) to the suspended ceiling plenum, (7) through a plurality of third dampers mounted between the suspended ceiling plenum and the heated air collection duct, and (8) into the heated air collection duct.

[0016] In a primary embodiment of the present invention, each of the first dampers, each of the second dampers, and each of the third dampers includes at least one mechanical thermostat mechanically connected to a series of louvers. Each mechanical thermostat is exposed to adjacent heated air having an adjacent temperature, and the mechanical thermostat is configured to increase or decrease the louver free area ratio of the series of louvers mechanically connected to the mechanical thermostat in response to each change in the adjacent temperature, whereby: (1) the mechanical thermostat is configured to increase the louver free area ratio of the series of louvers mechanically connected to the mechanical thermostat when the adjacent temperature of the mechanical thermostat is above a preset threshold temperature of the mechanical thermostat; and (2) the mechanical thermostat is configured to decrease the louver free area ratio of the series of louvers mechanically connected to the mechanical thermostat when the adjacent temperature of the mechanical thermostat is below the preset threshold temperature of the mechanical thermostat. Each first damper associated with each hot aisle is configured to (i) control a first variable airflow of the heated air from the hot aisle to the hot aisle duct associated with the hot aisle and (ii) preset a first thermostat setting. The first thermostat setting includes: (1) a first threshold temperature relative to a preset threshold temperature of the mechanical thermostat of the first damper, and (2) a first minimum louver free area ratio relative to a preset minimum louver free area ratio for the set of louvers of the first damper. Each second damper associated with each hot aisle duct is configured to (i) control a second variable airflow of the heated air from the hot aisle duct to the suspended ceiling plenum and (ii) preset a second thermostat setting. The second thermostat setting includes: (1) a second threshold temperature relative to a preset threshold temperature of the mechanical thermostat of the second damper, and (2) a second minimum louver free area ratio relative to a preset minimum louver free area ratio for the set of louvers of the second damper.Each third damper is configured to (i) control a third variable airflow of the heated air from the suspended ceiling plenum to the heated air collection duct and (ii) preset a third thermostat setting, the third thermostat setting including: (1) a third threshold temperature relative to a preset threshold temperature of the mechanical thermostat of the third damper, and (2) a third minimum louver free area ratio relative to a preset minimum louver free area ratio for the set of louvers of the third damper.

[0017] In another embodiment of the principal embodiment of the present invention, each hot aisle duct includes (i) an upper surface of the hot aisle duct HAD along a first horizontal plane, the first horizontal plane being coplanar with an upper surface of the suspended ceiling plenum FCP, and (ii) a lower surface of the hot aisle duct HAD along a second horizontal plane. The second horizontal plane is: (1) coplanar with the hot aisle ceiling associated with the hot aisle duct, and (2) coplanar with an underside of the suspended ceiling plenum FCP. Each of the first dampers of each hot aisle duct is mounted: (i) in the second horizontal plane, and (ii) between the hot aisle ceiling and the lower surface of the hot aisle duct HAD. Each of the second dampers of each hot aisle duct is mounted: (i) in at least one of a first vertical plane along a first vertical side of the hot aisle duct and a second vertical plane along a second vertical side of the hot aisle duct, and (ii) between the first vertical side or the second vertical side of the hot aisle duct and the suspended ceiling plenum.

[0018] In another embodiment of the principal embodiment of the present invention, each hot aisle duct includes (i) an upper surface of the hot aisle duct HAD along a second horizontal plane, the second horizontal plane being coplanar with an underside of the suspended ceiling plenum FCP, and (ii) a lower surface of the hot aisle duct HAD along a second alternate horizontal plane. The second alternate horizontal plane is: (1) coplanar with the hot aisle ceiling associated with the hot aisle duct, and (2) disposed parallel to the second horizontal plane and a third horizontal plane that is coplanar with a floor of the hot aisle associated with the hot aisle duct. Each first damper of each hot aisle duct is mounted: (i) within the second alternate horizontal plane, and (ii) between the hot aisle ceiling and the lower surface of the hot aisle duct HAD. Each of the second dampers in each hot aisle duct is mounted: (i) in the second horizontal plane, and (ii) between the upper surface of the HAD of the hot aisle duct and the lower surface of the FCP of the suspended ceiling plenum.

[0019] In addition to the technical elements of the first embodiment of the present invention, the second embodiment of the present invention further includes (a) for each row of server racks, at least one cooled air inlet to a cold aisle associated with the row of server racks, and (b) an air handling unit (AHU). The AHU is fluidly connected to (i) the heated air collection duct and (ii) the at least one cooled air inlet in each cold aisle. The AHU is configured to receive heated air through the heated air collection duct to generate cooled air. The at least one cooled air inlet is configured to receive the cooled air from the AHU.

[0020] In an alternative embodiment of the second embodiment of the present invention, the system further includes a free cooling tower and a chiller. The AHU includes a free cooling coil configured to receive a first free refrigerant flow from the free cooling tower. The AHU includes a trim cooling coil configured to receive a trim refrigerant flow from an evaporator passage of the chiller. In this embodiment, the chiller includes a condenser passage for receiving a second free refrigerant flow from the free cooling tower. In this embodiment, the free cooling tower can receive ambient air from an external environment in an ambient temperature range of 25°C to 32°C.

[0021] In an alternative embodiment of the second embodiment of the present invention, (a) the AHU further includes an AHU controller and a variable-speed fan, and (b) each branched heated air return path includes a plurality of networked temperature sensors. Each networked temperature sensor is configured to (i) detect a set of current local temperatures and (ii) transmit the set of current local temperatures to the AHU controller. The AHU controller is configured to (i) decrease the speed of the variable-speed fan of the AHU when at least one of the current local temperatures received from one of the networked temperature sensors is below a heated air threshold temperature, and (ii) increase the speed of the variable-speed fan of the AHU when at least one of the current local temperatures received from one of the networked temperature sensors is above a heated air threshold temperature. In this embodiment, the heated air threshold temperature can be selected from a heated air threshold temperature range of 38°C to 42°C.

[0022] The present invention is directed to creating a computer room cooling system that provides maximum energy efficiency for data computing centers located in tropical or other high humidity environments. The primary advantages of the present invention are achieved by maintaining a high delta temperature between (i) the temperature of the heated air received from the heated air collection duct and (ii) the temperature of the free tower refrigerant received from the free cooling tower.

[0023] The first damper is operative to regulate a first variable airflow between the hot aisle and the hot aisle duct, the first damper allowing the temperature of the heated air in the hot aisle to reach a first threshold temperature before a substantial portion of the heated air enters the hot aisle duct.

[0024] The second damper has a lower minimum louver free area ratio than the first damper. The first damper preferably has a minimum louver free area ratio in the range of 8 to 12 percent. The second damper preferably has a minimum louver free area ratio in the range of 0 to 3 percent. The second threshold temperature of the mechanical thermostat of the second damper can also be set to a preset thermostat temperature higher than the first threshold temperature of the mechanical thermostat of the first damper.

[0025] Therefore, if the heat generation rate by a row of server racks associated with a hot aisle duct is low, the heated air generated by that row of server racks is primarily restricted to the hot aisle volume and the first volume of the hot aisle duct. Airflow from this low heat generating row of server racks can proceed to the heated air collection duct via the first heated air return path.

[0026] On the other hand, if a particular row of server racks has a high heat generation rate, the excess heat can flow into the second volume of the suspended ceiling plenum. The suspended ceiling plenum thus acts as a thermal reservoir for the cooling system, tolerating variations in heat generation among the rows of server racks in the computer room. The third dampers allow heated air in the suspended ceiling plenum to enter the heated air collection duct (to complete the second heated air return path) only when the mechanical thermostats within these third dampers meet a third threshold temperature. The dampers thus allow dynamic adjustment of the total heated air reservoir volume for the computer room cooling system.

[0027] The AHU also features a variable-speed fan that can be slowed down to reduce the amount of heated air exhausted from the computer room when heat generation is low, and increased when heat generation is high. The AHU's variable-speed fan, along with the damper that creates a bifurcated heated air return path, provides a computer room cooling system that can maintain a more consistent, higher delta temperature between the temperature of the heated air drawn into the AHU and the temperature of the free tower refrigerant. This higher delta temperature increases the efficiency and benefits of the free tower refrigerant, thereby reducing reliance on the trim cooling coil to cool the heated air and reducing energy consumption by the chiller.

[0028] The mechanical thermostat damper design prevents a single point of failure, protecting the electronic equipment installed in the server rack row from excessive temperatures (e.g., temperatures above 40°C). If one of the primary dampers fails, heated air escapes from the hot aisle through the remaining functioning primary dampers. Additionally, the primary dampers preferably have a first minimum louver free area ratio in the range of 8 to 12 percent, minimizing the flow of heated air exiting the hot aisle. Mechanical thermostats are also independent of power and network communication. Therefore, the dampers are not affected by power outages or network failures.

[0029] Dampers can be easily installed in buildings not custom-designed to function as data computing centers. For example, existing perforated ceiling tiles in hot aisle ceilings can be replaced with a primary damper. For example, an existing suspended ceiling plenum can be used for a secondary heated air return path.

[0030] The present invention also improves the performance of prior art dual coil refrigeration systems by producing a higher delta temperature, such that the heated air passing through the hotter air handling unit is initially cooled to a greater extent by the first free refrigerant flow (from the free cooling tower) than if the heated air were cooler. [Effects of the Invention]

[0031] Overall, all technical aspects of the invention work together to maintain a high delta temperature, thereby maximizing the efficiency of free cooling towers in tropical or other high humidity environments. At the same time, the invention prevents overheating of electronic equipment in server racks and provides flexibility in computer room operation. [Brief explanation of the drawings]

[0032] [Figure 1] 1 is a block diagram illustrating a prior art heated air return path through a computer room. [Figure 2] FIG. 1 is a block diagram illustrating a prior art dual coil cooling system for a computer room using a free cooling tower and chiller. [Figure 3] FIG. 1 is a block diagram illustrating a prior art damper including a mechanical thermostat and a series of mechanically connected louvers. [Figure 4A] FIG. 10 is a block diagram illustrating an alternative bifurcated heated air return path design for the hot aisle duct in an alternative embodiment of the present invention. [Figure 4B] FIG. 10 is a block diagram illustrating an alternative bifurcated heated air return path design for the hot aisle duct in an alternative embodiment of the present invention. [Figure 5] FIG. 1 is a block diagram illustrating a bifurcated heated air return path design for a hot aisle duct in a horizontal plan view of a computer room in accordance with one embodiment of the present invention. [Figure 6] FIG. 2 is a block diagram illustrating, in simplified form, a first heated air return path and a second heated air return path for a computer room in one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0033] Embodiments of the present disclosure are hereinafter described herein with reference to the drawings.

[0034] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. The illustrative embodiments described in the detailed description, drawings, and claims are not intended to be limiting. Other embodiments may be utilized, and other changes may be made without departing from the spirit or scope of the subject matter presented herein. Unless otherwise specified, as used herein, the terms "comprising," "comprises," "including," and "comprises," as well as grammatical variations thereof, are intended to express open-closed or inclusive language such that the recited elements are included, but also permit the inclusion of additional, unrecited elements.

[0035] As described herein, a row of server racks may house various computing devices, such as servers and data storage devices, that generate heated air. The terms "planar" and "coplanar" are intended to describe cross-sectional volumes (either horizontal or vertical) within a computer room. These cross-sectional volumes may include, for example, the height of dampers, ceiling tiles, or flooring tiles. For example, "planar" and "coplanar" do not imply an idealized plane that has no volume.

[0036] As used herein, the term "damper" is not meant to be limited to any particular form factor. The dampers used in this invention may be purchased off-the-shelf or customized dampers of various dimensions. However, to ensure there is no single point of failure, the term "damper" is meant to describe individual, separate devices, each containing its own mechanical thermostat and set of louvers. In this way, if one or more dampers fail, the remaining dampers continue to function, reducing the likelihood of damage to electronic equipment mounted in rows of server racks. Dampers also have the advantage of enabling a rapid upgrade method for prior art computer rooms (e.g., by replacing perforated ceiling tiles in a hot aisle ceiling with a first damper).

[0037] 1-3 are described in the Background section of this specification.

[0038] 4A and 4B are block diagrams illustrating an alternative bifurcated heated air return path design for hot aisle duct 18 in a vertical plan side view of a computer room 15 according to an alternative embodiment of the present invention. As shown in FIGS. 1 and 2, the computer room 15 illustrated in FIGS. 4A and 4B includes a cold aisle 15A and a hot aisle 15B separated by a row of server racks 15C. Cold aisle 15A receives cooled air via raised-floor plenum inlet 15D1-a and / or fan wall inlet 15D1-b for cooling air inlet 15D1. The cooled air in cold aisle 15A is drawn through electronic equipment (e.g., servers and / or data storage devices) mounted in row of server racks 15C into hot aisle 15B where it is heated.

[0039] As with FIG. 2, FIGS. 4A and 4B identify several planar interfaces to aid in the description of items within the figures. The terms "plane" and "coplanar" used in this description are intended to describe cross-sectional volumes (either horizontal or vertical) within the computer room 15, rather than ideal planes that have no volume. The first horizontal plane 21 is coplanar with the upper surface of the FCP of the suspended ceiling plenum 16. The second horizontal plane 22-a is coplanar with the lower surface of the FCP of the suspended ceiling plenum 16, the cold aisle ceiling 15A1 of the cold aisle 15A, and the hot aisle ceiling 15B1 of the hot aisle 15B. The third horizontal plane 23 is coplanar with the upper surface of the raised floor plenum 17. The fourth horizontal plane 24 is coplanar with the lower surface of the raised floor plenum 17. The first vertical plane 31 is coplanar with the first side of the hot aisle 15B. The second vertical plane 32 is coplanar with the second side of the hot aisle 15B. The third vertical plane 33 is flush with one side edge of the suspended ceiling plenum 16 .

[0040] 4A and 4B, heated air in hot aisle 15B is drawn into hot aisle duct 18 through first damper 20A (see arrow 20A1) mounted in hot aisle ceiling 15B1 along second horizontal plane 22-a, replacing the perforated ceiling tiles of the prior art design detailed in Figure 1. The heated air can return to air handling unit 14 (not shown) along the length of hot aisle duct 18 in first heated air return path 61 (see also Figure 5 for a top view of computer room 15). The heated air can also return to AHU 14 (not shown) in a second heated air return path 62, starting from hot aisle duct 18, passing through second damper 20B (mounted on first vertical plane 31, see arrow 20B1), then into suspended ceiling plenum 16, through third damper 20C (mounted on third vertical plane 33, see arrow 20C1), into heated air collection duct (HACD) 14C, and finally into heated air outlet 15D2 (not shown). Cold aisle 15A receives cooled air via raised floor plenum inlet 15D1-a and / or fan wall inlet 15D1-b for cooled air inlet 15D1.

[0041] In the embodiment of the present invention shown in FIG. 4A , the hot aisle ducts 18 include an upper surface of the hot aisle duct 18's HAD along a first horizontal plane and a lower surface of the hot aisle duct 18's HAD along a second horizontal plane 22-a. The second horizontal plane 22-a is flush with the hot aisle ceiling 15B1 associated with the hot aisle duct 18. For example, when retrofitting an industrial office location to use the embodiment of the present invention shown in FIG. 4A , the hot aisle ducts 18 are installed within an existing suspended ceiling plenum 16. A first damper 20A of each of the hot aisle ducts 18 is installed in the second horizontal plane 22-a between the hot aisle ceiling 15B1 and the lower surface of the hot aisle duct 18's HAD. A second damper 20B is installed on the first vertical side of the hot aisle duct 18 in the first vertical plane 31, between the first vertical side of the hot aisle duct 18 and a first portion of the suspended ceiling plenum 16.

[0042] Although not shown in Figure 4A (see the top view of this embodiment shown in Figure 5), the second dampers 20B of the hot aisle duct 18 may also be mounted in the second vertical plane 32 along the second vertical side of the hot aisle duct 18. These second dampers 20B are mounted between the second vertical side of the hot aisle duct 18 and the second portion of the suspended ceiling plenum 16 (not shown in Figure 4A but see the top view of this embodiment shown in Figure 5).

[0043] The third damper 20C is mounted in a third vertical plane 33 between the suspended ceiling plenum 16 and the heated air collection duct 14C.

[0044] In the embodiment of the present invention shown in FIG. 4B, the hot aisle ducts 18 include an upper surface of the hot aisle duct's 18 HAD along a second horizontal plane 22-a and a lower surface of the hot aisle duct's 18 HAD along a second alternate horizontal plane 22-b. The second alternate horizontal plane 22-b is flush with the hot aisle ceiling 15B1 associated with the hot aisle duct 18. The first damper 20A of each hot aisle duct 18 is attached to the second alternate horizontal plane 22-b between the hot aisle ceiling 15B1 and the lower surface of the hot aisle duct's 18 HAD. For example, in the embodiment of the present invention shown in FIG. 4B, the hot aisle ceiling 15B1 is lowered and the hot aisle ducts 18 are attached below the suspended ceiling plenum 16. The second damper 20B of each hot aisle duct 18 is attached to the second horizontal plane 22-a between the upper surface of the hot aisle duct's 18 HAD and the lower surface of the suspended ceiling plenum 16.

[0045] FIG. 5 is a block diagram illustrating a bifurcated heated air return path design for hot aisle duct 18 in the embodiment of the invention shown in FIG. 4A in a horizontal plan view of computer room 15.

[0046] Similar to FIGS. 2, 4A, and 4B, FIG. 5 identifies several planar interfaces to aid in the description of the items in the figure. The terms "planar" and "coplanar" used in this description are intended to describe cross-sectional volumes within computer room 15, rather than ideal planes that have no volume. First vertical plane 31 is coplanar with a first side of hot aisle 15B. Second vertical plane 32 is coplanar with a second side of hot aisle 15B. Third vertical plane 33 is coplanar with one side edge of suspended ceiling plenum 16. FIG. 5 introduces a fourth vertical plane 34 along the right side of the figure.

[0047] 4A and 4B, in FIG. 5, heated air in hot aisle 15B is drawn into hot aisle duct 18 through first damper 20A (not shown, see FIG. 4A and arrow 20A1). The heated air can return to AHU 14 (not shown) along the length of hot aisle duct 18 in first heated air return path 61. The heated air can also pass through second damper 20B (mounted on first vertical plane 31, see arrow 20B1) into a first portion of suspended ceiling plenum 16, through third damper 20C (mounted on third and fourth vertical planes 33 and 34, see arrow 20C1), into heated air collection duct (HACD) 14C and heated air outlet 15D2, and then return from hot aisle duct 18 to AHU 14 (not shown) through second heated air return path 62.

[0048] Similar to Figure 4A, the second dampers 20B in Figure 5 are mounted to a first vertical side of the hot aisle duct 18 in a first vertical plane 31. The second dampers 20B in the hot aisle duct 18 are also shown in Figure 5 as being mounted in a second vertical plane 32 along a second vertical side of the hot aisle duct 18. These second dampers 20B are mounted between the second vertical side of the hot aisle duct 18 and a second portion of the suspended ceiling plenum 16.

[0049] The third damper 20C is mounted in a third vertical plane 33 and a fourth vertical plane 34 between the suspended ceiling plenum 16 and the heated air collection duct 14C.

[0050] 5 is not drawn to scale. In particular, the first volume of each hot aisle duct 18 is preferably less than 25 percent of the second volume of the suspended ceiling plenum 16.

[0051] 6 is a block diagram 6-00 illustrating, in simplified form, a first heated air return path 61 and a second heated air return path 62 for a computer room 15 in one embodiment of the present invention. The first heated air return path 61 travels from the row of server racks 15C into the hot aisle 15B, through a first damper 20A (see arrow 20A1), into the hot aisle duct 18, and to the heated air collection duct 14C. The second heated air return path 62 travels from the row of server racks 15C into the hot aisle 15B, through the first damper 20A (see arrow 20A1), into the hot aisle duct 18, through the second damper 20B (see arrow 20B1), into the suspended ceiling plenum 16, through the third damper 20C (see arrow 20C1), and into the heated air collection duct 14C. The heated air from the first heated air return path 61 and the second heated air return path 62 is led to the air handling unit (AHU) 14 via the heated air outlet 15D2.

[0052] Heated air collected from the first heated air return path 61 and the second heated air return path 62 is directed to the AHU 14. The AHU 14 includes a variable speed fan 14D, a free cooling coil 14A, and a trim cooling coil 14B. The cooled air from the AHU 14 is directed to the cold aisle 15A via a raised floor plenum inlet 15D1-a and / or a fan wall inlet 15D1-b.

[0053] In its most general form, the present invention is a computer room cooling system including multiple branched heated air return paths for heated air generated by multiple rows of server racks 15C operating within a computer room 15 having a suspended ceiling plenum 16 and a heated air collection duct 14C. A first heated air return path 61 routes heated air from a hot aisle duct 18 to the heated air collection duct 14C. A second heated air return path 62 routes heated air from the hot aisle duct 18 to a suspended ceiling plenum 16 of predetermined volume before the heated air is routed to the heated air collection duct 14C. A damper 20 with a mechanical thermostat 22 is used to control airflow between the hot aisle duct 18 and the suspended ceiling plenum 16 of predetermined volume. The present invention can be used to maintain a minimum delta temperature between the heated air and a first free refrigerant flow received by an air handling unit (AHU) 14 from a free cooling tower 11 operating in a high-humidity exterior environment.

[0054] A primary embodiment of the present invention is a computer room cooling system including multiple branched heated air return paths for heated air generated by multiple server rack rows 15C operating within a computer room 15 having a suspended ceiling plenum 16 and a heated air collection duct 14C. Each branched heated air return path corresponds to one server rack row 15C in the computer room 15, one hot aisle 15B adjacent to the one server rack row 15C, and one hot aisle duct 18 located in the ceiling of the one server rack row 15B. Further, each branched heated air return path includes (i) a first heated air return path 61 for heated air generated by one server rack row 15C and (ii) a second heated air return path 62 for heated air generated by one server rack row 15C. The first heated air return path 61 proceeds as follows: The second heated air return path 62 proceeds as follows: (1) from one server rack row 15C associated with the branched heated air return path, (2) into one hot aisle 15B located adjacent to one server rack row 15C, (3) through a plurality of first dampers 20A (see arrow 20A1) attached to the ceiling of one hot aisle 15B, (4) into one hot aisle duct 18 located above the ceiling of one hot aisle 15B, and (5) into the heated air collection duct 14C. (1) from one server rack row 15C associated with the branched heated air return path, (2) into one hot aisle 15B located adjacent to one server rack row 15C, (3) through a plurality of first dampers 20A (see arrow 20A1) attached to the ceiling of one hot aisle 15B, (4) into one hot aisle duct 18 located above the ceiling of one hot aisle 15B, (5) through a plurality of second dampers 20B (see arrow 20B1) attached to the side or top of one hot aisle duct 18, (6) into the suspended ceiling plenum 16, (7) through a plurality of third dampers 20C (see arrow 20C1) attached between the suspended ceiling plenum 16 and the heated air collection duct 14C, (8) into the heated air collection duct 14C.

[0055] In a primary embodiment of the present invention, each of the first dampers 20A, each of the second dampers 20B, and each of the third dampers 20C includes at least one mechanical thermostat 22 mechanically connected to a series of louvers 21. Each mechanical thermostat 22 is exposed to adjacent heated air having an adjacent temperature, and the mechanical thermostat 22 is configured to increase or decrease the louver free area ratio of the series of louvers 21 mechanically connected to the mechanical thermostat 22 in response to each change in the adjacent temperature, so that: (1) the mechanical thermostat 22 is configured to increase the louver free area ratio of the series of louvers 21 mechanically connected to the mechanical thermostat 22 when the adjacent temperature of the mechanical thermostat 22 exceeds a preset threshold temperature of the mechanical thermostat 22, and (2) the mechanical thermostat 22 is configured to decrease the louver free area ratio of the series of louvers 21 mechanically connected to the mechanical thermostat 22 when the adjacent temperature of the mechanical thermostat 22 is below the preset threshold temperature of the mechanical thermostat 22. Each first damper 20A associated with each hot aisle 15B is configured to (i) control a first variable airflow of heated air from the hot aisle 15B into the hot aisle duct 18 associated with the hot aisle 15B and (ii) preset a first thermostat setting. The first thermostat setting includes: (1) a first threshold temperature relative to a preset threshold temperature of the mechanical thermostat 22 of the first damper 20A, and (2) a first minimum louver free area ratio relative to a preset minimum louver free area ratio for the set of louvers 21 of the first damper 20A. Each second damper 20B associated with each hot aisle duct 18 is configured to (i) control a second variable airflow of heated air from the hot aisle duct 18 to the suspended ceiling plenum 16 and (ii) preset a second thermostat setting. The second thermostat settings include: (1) a second threshold temperature relative to a preset threshold temperature of the mechanical thermostat 22 of the second damper 20B, and (2) a second minimum louver free area ratio relative to a preset minimum louver free area ratio for the set of louvers 21 of the second damper 20B.Each third damper 20C is configured to (i) control a third variable airflow of heated air from the suspended ceiling plenum 16 to the heated air collection duct 14C and (ii) preset a third thermostat setting, which includes: (1) a third threshold temperature relative to a preset threshold temperature of the mechanical thermostat 22 of the third damper 20C, and (2) a third minimum louver free area ratio relative to a preset minimum louver free area ratio for the set of louvers 21 of the third damper 20C.

[0056] In another embodiment of the principal embodiment of the present invention, each hot aisle duct 18 includes (i) an upper surface of the HAD of the hot aisle duct 18 along a first horizontal plane 21, the first horizontal plane 21 being coplanar with an upper surface of the FCP of the suspended ceiling plenum 16, and (ii) a lower surface of the HAD of the hot aisle duct 18 along a second horizontal plane 22-a. The second horizontal plane 22-a is: (1) coplanar with the hot aisle ceiling 15B1 associated with the hot aisle duct 18, and (2) coplanar with the lower surface of the FCP of the suspended ceiling plenum 16. Each of the first dampers 20A of each hot aisle duct 18 is mounted: (i) within the second horizontal plane 22-a, and (ii) between the hot aisle ceiling 15B1 and the lower surface of the HAD of the hot aisle duct 18. Each of the second dampers 20B of each hot aisle duct 18 is attached: (i) to at least one of a first vertical plane 31 along a first vertical side of the hot aisle duct 18 and a second vertical plane 32 along a second vertical side of the hot aisle duct 18, and (ii) between the first vertical side or the second vertical side of the hot aisle duct 18 and the suspended ceiling plenum 16.

[0057] In another embodiment of the principal embodiment of the present invention, each hot aisle duct 18 includes (i) an upper surface of the HAD of the hot aisle duct 18 along a second horizontal plane 22-a, where the second horizontal plane 22-a is coplanar with the lower surface of the FCP of the suspended ceiling plenum 16, and (ii) a lower surface of the HAD of the hot aisle duct 18 along a second alternate horizontal plane 22-b. The second alternate horizontal plane 22-b: (1) is coplanar with the hot aisle ceiling 15B1 associated with the hot aisle duct 18, and (2) is positioned parallel to and between the second horizontal plane 22-a and a third horizontal plane that is coplanar with the floor of the hot aisle 15B associated with the hot aisle duct 18. Each of the first dampers 20A of each hot aisle duct 18 is mounted: (i) in the second alternative horizontal plane 22-b, and (ii) between the hot aisle ceiling 15B1 and the underside of the HAD of the hot aisle duct 18. Each of the second dampers 20B of each hot aisle duct 18 is mounted: (i) in the second horizontal plane 22-a, and (ii) between the upper surface of the HAD of the hot aisle duct 18 and the underside of the FCP of the suspended ceiling plenum 16.

[0058] In another embodiment of the main embodiment of the present invention, the third damper 20C is mounted: (a) in a third vertical plane 33 along at least one edge side of the suspended ceiling plenum 16, and (b) between the suspended ceiling plenum 16 and the heated air collection duct 14C.

[0059] In another embodiment of the principal embodiment of the present invention, the first volume of each hot aisle duct 18 is less than 25 percent of the second volume of the suspended ceiling plenum 16 .

[0060] In another embodiment of the main embodiment of the present invention: (a) the first threshold temperature is selected from a first threshold temperature range of 35°C to 39°C, and (b) the second threshold temperature is selected from a second threshold temperature range of 37°C to 41°C.

[0061] In another embodiment of the principal embodiment of the present invention, the first minimum louver free area percentage is within a first free area range of 8 to 12 percent.

[0062] In another embodiment of the principal embodiment of the present invention, the second minimum louver free area percentage is within a second free area range of 0 to 3 percent.

[0063] In another embodiment of the main embodiment of the present invention, (a) the maximum louver free area ratio of each of the first dampers 20A, each of the second dampers 20B, and each of the third dampers 20C is within a maximum free area range of 25 to 35 percent, (b) each of the mechanical thermostats 22 has an adjacent temperature response time of less than 15 seconds, and (c) each of the mechanical thermostats 22 has an optimized temperature response range of 30°C to 45°C.

[0064] In another embodiment of the main embodiment of the present invention, at least one mechanical thermostat 22 associated with each series of louvers 21 is mounted upstream of the series of louvers 21 .

[0065] In addition to the technical elements of the first embodiment of the present invention, the second embodiment of the present invention further includes (a) at least one cooled air inlet 15D1 for each server rack row 15C into the cold aisle 15A associated with the server rack row 15C, and (b) an air handling unit (AHU) 14. The AHU 14 is fluidly connected to (i) the heated air collection duct 14C and (ii) the at least one cooled air inlet 15D1 in each cold aisle 15A. The AHU 14 is configured to receive heated air via the heated air collection duct 14C to generate cooled air. The at least one cooled air inlet 15D1 is configured to receive the cooled air from the AHU 14.

[0066] In another embodiment of the second embodiment of the present invention, (a) the cooled air taken into each cold aisle 15A from the AHUs 14 is within a cooled air temperature range of 23°C to 27°C, and (b) the heated air received by the AHUs 14 via the heated air collection ducts (HACDs) 14C is within a heated air temperature range of 38°C to 42°C.

[0067] In another embodiment of the second embodiment of the present invention, the system further includes a free cooling tower 11 and a chiller 13. The AHU 14 includes a free cooling coil 14A configured to receive a first free refrigerant stream from the free cooling tower 11. The AHU 14 includes a trim cooling coil 14B configured to receive a trim refrigerant stream from an evaporator passage 13B of the chiller 13. In this embodiment, the chiller 13 may include a condenser passage 13A for receiving a second free refrigerant stream from the free cooling tower 11. In this embodiment, the free cooling tower 11 may receive ambient air 12 from an external environment in an ambient temperature range of 25°C to 32°C.

[0068] In an alternative embodiment of the second embodiment of the present invention, (a) the AHU 14 further includes an AHU controller and a variable-speed fan 14D, and (b) each branched heated air return path includes a plurality of networked temperature sensors. Each networked temperature sensor is configured to (i) detect a set of current local temperatures and (ii) transmit the set of current local temperatures to the AHU controller. The AHU controller is configured to (i) decrease the speed of the variable-speed fan 14D of the AHU 14 when at least one of the current local temperatures received from one of the networked temperature sensors is below a heated air threshold temperature, and (ii) increase the speed of the variable-speed fan 14D of the AHU 14 when at least one of the current local temperatures received from one of the networked temperature sensors is above the heated air threshold temperature. In this embodiment, the heated air threshold temperature can be selected from a heated air threshold temperature range of 38°C to 42°C.

[0069] While various aspects and embodiments have been disclosed herein, it will be apparent that various other modifications and adaptations of the present invention will become apparent to those skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention, and all such modifications and adaptations are intended to be within the scope of the appended claims. The various aspects and embodiments disclosed herein are for illustrative purposes and are not intended to be limiting, with the true scope and spirit of the invention being indicated by the appended claims. [Explanation of symbols]

[0070] 10. Dual coil cooling system 11 Free cooling tower 12 Ambient air 13 Chiller 13A Condenser passage 13B Evaporator passage 14 Air Handling Unit (AHU) 14A free cooling coil 14B Trim cooling coil 14C Heated Air Collection Duct (HACD) 14D Variable Speed Fan 15 Computer Room 15A Cold Aisle 15A1 Cold aisle ceiling 15B Hot Aisle 15B1 Hot aisle ceiling 15C Server Rack Row 15D1 Cooling air inlet 15D1-a Raised floor plenum inlet 15D1-b Fan wall inlet 15D2 Heated air outlet 16 Suspended Ceiling Plenum (FCP) 17 Raised floor plenum 18 Hot aisle duct (HAD) 20 Damper 20A First Damper 20A1 First variable outflow 20B Second damper 20B1 Second variable outflow 20C Third Damper 20C2 Third variable outflow 20-X Damper Side View 20-Y Damper End View 20-Z damper bottom view 21 First horizontal plane 21 series of louvers 22 Mechanical Thermostat 22-a Second horizontal plane 22-b Second Alternate Horizontal Plane 23 Third horizontal plane 24 Fourth horizontal plane 31 First vertical plane 32 Second vertical plane 33 Third Vertical Plane 34 Fourth Vertical Plane 61 First heated air return path 62 Second heated air return path

Claims

1. 1. A computer room cooling system having a plurality of branched heated air return paths for heated air generated by a plurality of rows of server racks operating in a computer room having a suspended ceiling plenum and a heated air collection duct, comprising: (a) each branched heated air return path is associated with one row of server racks in the computer room, one hot aisle disposed adjacent to the one row of server racks, and one hot aisle duct disposed on the ceiling of the one hot aisle, and further each branched heated air return path is (i) a first heated air return path for heated air generated by the one row of server racks, comprising: (1) from the one row of server racks associated with the branched heated air return path; (2) entering one hot aisle located adjacent to the one row of server racks; (3) via a plurality of first dampers attached to the ceiling of the one hot aisle; (4) into one hot aisle duct located above the ceiling of said one hot aisle; and (5) into the heated air collection duct; a first heated air return path; (ii) a second heated air return path for the heated air generated by the one row of server racks, (1) from the one row of server racks associated with the branched heated air return path; (2) entering one hot aisle located adjacent to the one row of server racks; (3) via a plurality of first dampers attached to the ceiling of the one hot aisle; (4) into one hot aisle duct located above the ceiling of said one hot aisle; (5) via a plurality of second dampers attached to the side or top of the one hot aisle duct; (6) to said suspended ceiling plenum; (7) via a plurality of third dampers mounted between the suspended ceiling plenum and the heated air collection duct; and (8) into the heated air collection duct; a second heated air return path; Including, (b) each of the first dampers, each of the second dampers, and each of the third dampers includes at least one mechanical thermostat mechanically connected to a series of louvers; (i) each mechanical thermostat is exposed to adjacent heated air having an adjacent temperature, and the mechanical thermostat is configured to increase or decrease a louver free area ratio of the set of louvers mechanically connected to the mechanical thermostat in response to each change in the adjacent temperature, thereby: (1) the mechanical thermostat is configured to increase a free louver area ratio of the set of louvers mechanically connected to the mechanical thermostat when the adjacent temperature of the mechanical thermostat exceeds a preset threshold temperature of the mechanical thermostat; (2) the mechanical thermostat is configured to reduce a free louver area ratio of the set of louvers mechanically connected to the mechanical thermostat when the adjacent temperature of the mechanical thermostat is below the preset threshold temperature; (c) each first damper associated with each hot aisle: (i) controlling a first variable airflow of the heated air from the hot aisle to the hot aisle duct associated with the hot aisle; and (ii) presetting a first thermostat setting; The first thermostat setting is: (1) a first threshold temperature relative to a preset threshold temperature of the mechanical thermostat of the first damper; and (2) a first minimum louver free area ratio relative to a preset minimum louver free area ratio for the set of louvers of the first damper; Including, (d) each second damper associated with each hot aisle duct: (i) controlling a second variable airflow of the heated air from the hot aisle duct to the suspended ceiling plenum; and (ii) presetting a second thermostat setting; The second thermostat setting is: (1) a second threshold temperature relative to the preset threshold temperature of the mechanical thermostat of the second damper; and (2) a second minimum louver free area ratio relative to a preset minimum louver free area ratio for the set of louvers of the second damper; Including, (e) each third damper: (i) controlling a third variable air flow of the heated air from the suspended ceiling plenum to the heated air collection duct; and (ii) presetting a third thermostat setting; The third thermostat setting is: (1) a third threshold temperature relative to the preset threshold temperature of the mechanical thermostat of the third damper; and (2) a third minimum louver free area ratio relative to a preset minimum louver free area ratio for the set of louvers of the third damper; Including, system.

2. 10. The system of claim 1, (a) Each hot aisle duct: (i) a HAD upper surface of a hot aisle duct along a first horizontal plane, the first horizontal plane being coplanar with an FCP upper surface of the suspended ceiling plenum; (ii) a lower surface of the hot aisle duct HAD along a second horizontal plane; and the second horizontal plane includes: (1) flush with the hot aisle ceiling associated with the hot aisle duct; and (2) flush with the underside of the FCP of said suspended ceiling plenum; Located in (b) each of the first dampers in each hot aisle duct: (i) the second horizontal surface; and (ii) between the hot aisle ceiling and the underside of the HAD of the hot aisle duct; It is attached to (c) each of the second dampers in each hot aisle duct comprising: (i) at least one of a first vertical plane along a first vertical side of the hot aisle duct and a second vertical plane along a second vertical side of the hot aisle duct; and (ii) between the first vertical side or the second vertical side of the hot aisle duct and the suspended ceiling plenum; Attached to system.

3. 10. The system of claim 1, (a) Each hot aisle duct: (i) an upper surface of the HAD of the hot aisle duct along a second horizontal plane, the second horizontal plane being coplanar with an FCP lower surface of the suspended ceiling plenum; and (ii) a lower surface of the hot aisle duct HAD along a second alternative horizontal plane; The second alternative horizontal plane is: (1) is flush with the hot aisle ceiling associated with the hot aisle duct; and (2) the hot aisle duct is disposed parallel to the second horizontal plane and a third horizontal plane that is flush with the floor of the hot aisle associated with the hot aisle duct; (b) each of the first dampers in each hot aisle duct: (i) a second alternative horizontal plane; and (ii) between the hot aisle ceiling and the underside of the HAD of the hot aisle duct; It is attached to (c) each of the second dampers in each hot aisle duct comprising: (i) a second horizontal surface; and (ii) between the upper surface of the HAD of the hot aisle duct and the lower surface of the FCP of the suspended ceiling plenum; Attached to system.

4. 10. The system of claim 1, The third damper comprises: (a) a third vertical plane along at least one edge side of the suspended ceiling plenum; and (b) between the suspended ceiling plenum and the heated air collection duct; The system is installed in.

5. 10. The system of claim 1, The system wherein the first volume of each hot aisle duct is less than 25 percent of the second volume of the suspended ceiling plenum.

6. 10. The system of claim 1, (a) the first threshold temperature is selected from a first threshold temperature range of 35°C to 39°C; (b) the second threshold temperature is selected from a second threshold temperature range of 37°C to 41°C.

7. 10. The system of claim 1, The system wherein the first minimum louver free area percentage is within a first free area range of 8 to 12 percent.

8. 10. The system of claim 1, The system wherein the second minimum louver free area percentage is within a second free area range of 0 to 3 percent.

9. 10. The system of claim 1, (a) a maximum louver free area ratio of each of the first dampers, each of the second dampers, and each of the third dampers is within a maximum free area range of 25 to 35 percent; (b) each of said mechanical thermostats has a proximal temperature response time of less than 15 seconds; (c) each of the mechanical thermostats has an optimized temperature response range of 30°C to 45°C; system.

10. 10. The system of claim 1, The at least one mechanical thermostat associated with each series of louvers is mounted upstream of the series of louvers.

11. A system according to any one of claims 1 to 10, comprising: (a) for each row of server racks, at least one cooling air inlet to a cold aisle associated with the row of server racks; (b) an air handling unit (AHU); Further comprising: The air handling unit (AHU) comprises: (i) the heated air collection duct, the heated air collection duct configured to receive heated air through the heated air collection duct to generate cooled air; and (ii) the at least one cooled air inlet in each cold aisle, the at least one cooled air inlet configured to receive the cooled air from the AHU; and a system that is fluidly connected to the

12. 12. The system of claim 11, (a) the chilled air taken into each cold aisle from the AHU is within a chilled air temperature range of 23°C to 27°C; and (b) the heated air received by the AHU through the heated air collection duct is in a heated air temperature range of 38°C to 42°C; system.

13. 12. The system of claim 11, The system further includes a free cooling tower and a chiller; (a) the AHU includes a free cooling coil configured to receive a first free refrigerant flow from the free cooling tower; (b) the AHU includes a trim cooling coil configured to receive a trim refrigerant flow from an evaporator passage of the chiller; system.

14. 14. The system of claim 13, The chiller includes a condenser passageway that receives a second free refrigerant flow from the free cooling tower.

15. 14. The system of claim 13, The system wherein the free cooling tower receives ambient air from an external environment having an ambient temperature range of 25°C to 32°C.

16. 12. The system of claim 11, (a) the AHU further includes an AHU controller and a variable speed fan; (b) each branched heated air return path includes a plurality of networked temperature sensors, each networked temperature sensor comprising: (i) detecting a set of current local temperatures; and (ii) sending a set of current local temperatures to the AHU controller; It is structured as follows: (c) the AHU controller: (i) reducing the speed of a variable speed fan of the AHU when at least one of the current local temperatures received from one of the networked temperature sensors is below a heated air threshold temperature; and (ii) increasing the speed of a variable speed fan of the AHU when at least one of the current local temperatures received from one of the networked temperature sensors is above a heated air threshold temperature; The system is configured as follows:

17. 17. The system of claim 16, The heated air threshold temperature is selected from a heated air threshold temperature range of 38°C to 42°C.

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